A granular permissions' backend for Django

A granular permissions' backend for Django

# A granular permissions' backend for Django

try:
    set
except NameError:
    from sets import Set as set # Python 2.3 fallback

from django.contrib.auth.backends import ModelBackend

class PermissionsBackend(ModelBackend):
    """
    Checks granular permissions.
    """
    supports_object_permissions = True

    def get_group_permissions(self, user_obj, instance=None):
        """
        Returns a set of permission strings that this user has through his/her
        groups.
        """
        if instance is not None:
            # TODO
            return set()
        else:
            return super(PermissionsBackend, self).get_group_permissions(user_obj)

    def get_all_permissions(self, user_obj, instance=None):
        if instance is not None:
            # TODO
            return set()
        else:
            return super(PermissionsBackend, self).get_all_permissions(user_obj)

    def has_perm(self, user_obj, perm, instance=None):
        return perm in self.get_all_permissions(user_obj, instance)